Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. Accordingly, electric power generation and power storage based on an electrochemical reaction have been among the most active fields of research.
A secondary battery is a typical example of an electrochemical device utilizing such electrochemical energy currently being used, and the application area thereof is gradually increasing. With the recent technology development and increased demand for mobile devices such as portable computers, mobile telephones, and cameras, the demand for secondary batteries as the energy source thereof is rapidly increasing. Among such secondary batteries, lithium secondary batteries which exhibit high energy density and high operating potential and have a long cycle life and a low self-discharge rate have been frequently researched and extensively used commercially.
Conventional secondary batteries have been used for various purposes, and efforts have been made to produce batteries having various advantageous characteristics such as high capacity, high output, a long life, and high-speed charging. In producing a battery having the advantage of high capacity among those listed above, the most important thing is how much active material can be included in the battery.
Hence, there is a method of producing a battery having high capacity and high output by increasing an active material content and lowering a binder content, and, in order to obtain an electrode exhibiting the same levels of adhesion and phase stability even with a low binder content, a binder having a high molecular weight or high degree of substitution is used.
However, a solution containing a binder having a high molecular weight or a high degree of substitution dissolved therein has a higher viscosity and higher elasticity compared to a solution containing a binder having a lower molecular weight or a lower degree of substitution at the same binder content. Therefore, there is a problem that active material particles, a conductive material, etc. are not easily dispersed in a solvent by the same dispersion method. When more solvent is added to reduce the binder content and thereby solve the above problem, an electrode slurry with a lower solid content is obtained. In this case, a battery with a lower capacity is produced, and drying conditions become difficult, resulting in cost disadvantages.
Accordingly, it is required to develop an electrode slurry that has a high viscosity and includes well-dispersed particles such as those of an active material and a conductive material, and thus can be applied with a large thickness to produce an electrode.